German patent DE-PS 36 00 408 shows a reciprocating internal combustion engine having three intake valves per cylinder, wherein each of the three intake passages to the valves has a throttle valve in order to achieve an optimal filling and charge motion in each cylinder for each operating range. The three individual intake systems are designed or adapted to one another in accordance with the requirements for various engine speed ranges. The combustion air is conveyed by an intake manifold and separate intake passages issuing therefrom, to the individual charging ducts provided with throttle valves. The valves are built into the charging ducts inside the cylinder head in order to influence the partial-load behavior. These features, however, require sufficient space relationships, which are not always available in engine designs. Additionally, a multiplicity of individual parts are required, thus making the design expensive and more susceptible to malfunctions.
The inclusion of the valves in the respective intake lines shortly ahead of the cylinder also leads to corresponding problems, in addition to which there are manufacturing problems as well as a reduction in the passage cross section even when the valve is fully opened.